1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio receivers used in such wireless communication systems.
2. Description of Related Art
Radio receivers are known to receive radio frequency (RF) signals and convert them to baseband, or near baseband, signals that are subsequently demodulated to recapture transmitted data. The accuracy in which the transmitted data is recaptured is dependent on the radio receiver's ability to distinguish the desired signals from undesired signals and noise. For example, in an IEEE 802.11a compliant radio receiver, the transmitted data may be transmitted on a particular channel, where other channels may interfere with the receiver's ability to process the signals on the desired channel. Further difficulties arise when the signal strength of the desired signals are weak, thus yielding a low signal to noise and/or interferer ratio.
As is known, the signal strength of the desired signals varies based on transmit power of the transmitter, distance between the receiver and the transmitter, and multi-path fading. As is also known, multi-path fading occurs when the receiver is in a physical location where the multiple wireless paths from the transmitter to the receiver substantially cancel one another, even though the signal strength of many of the paths may be relatively strong.
To combat the adverse effects of multi-path fading, many receivers include a diversity antenna, which includes two or more antennas spaced one-half wavelength or more apart. With such spacing, one antenna may be experiencing significant multi-path fading, while another antenna will be experiencing much less multi-path fading. Thus, the receiver selects the signals received via the antenna experiencing the least amount of multi-path fading.
While such use of diversity antennas reduces the adverse effects of multi-path fading, it does so by discarding the signals received via the other antenna, or antennas. In many instances, the multi-path fading does not significantly adversely affect all of the subcarriers of a channel, but only a few subcarriers. Thus, by discarding the entire signal, some useful information is being ignored, which, if used, could improve the receiver's ability to accurately recapture the transmitted data.
Therefore, a need exists for a method and apparatus of a radio receiver that includes a diversity antenna structure that improves the receiver's accuracy by using information from multiple antennas.